1. Field of the Invention
The present invention relates to a contact probe used as a probe pin, or a socket pin etc., for electrical testing of devices, such as semiconductor IC (Integrated Circuit) chips, liquid crystal devices, etc., and more particularly to a contact probe integrated into a probe card, a probe device, a test socket, etc. and which are brought into contact with respective terminals of a device under test.
2. Description of Related Art
Contact pins are generally used for carrying out an electrical testing by being brought into contact with respective terminals of a device under test, for example, such as a semiconductor chip, such as an IC chip, an LSI (Large Scale Integrated Circuit) chip, an LCD (Liquid Crystal Display), etc.
In recent years, with high integration and miniaturization of devices, such as IC chips etc., contact pads configured as electrodes formed with a narrow pitch, multi pins, and narrow pitch contact pins have been required. According to one solution to the above requirements, a contact probe made of tungsten needles used as contact pins has been proposed. However; with this solution it is difficult to deal with multi pins and narrow pitch requirements due to a limitation in the diameter of the tungsten needles.
In Japanese Examined Patent Publication No. JP-B-7-82027, a contact probe technology where a plurality of wiring patterns are formed on a resin film and respective front end portions of the wiring patterns are arranged to project from the resin film to form contact pins is proposed. According to this technology, a probe device having multi pins and narrow pitch is possible and numerous complex parts are not required as compared to other technologies. As shown in FIG. 110, a conventional contact probe 1A has a structure where wiring patterns 3A formed from Ni (nickel) or a Ni alloy are attached on one face of a polyimide resin film 2A and front end portions of the wiring patterns 3A are projected from an end portion of the resin film 2A so as to form contact pins 3aA. In FIG. 110, positioning holes 4A are formed in the polyimide resin film 2A as will be described later.
Japanese Unexamined Patent Publication No. JP-A-6-324081 proposes a probe device (probe card) using contact probes having a flexible substrate, as in the previously discussed publication, where front end portions of wiring patterns constitute contact pins. According to this probe device, a matching is conducted with respect to a difference in pin pitches of an IC chip or device under test, etc. and a tester. The proposed probe device is suitable for probe testing an IC chip etc. having multi pins and narrow pitch.
FIGS. 111–113 will now be used to explain the operation of a conventional probe device 11A where a contact probe 1A is integrated with a mechanical parts 10A. The mechanical parts 10A include a mounting base 12A, a top clamp 13A and a bottom clamp 14A. The probe device 11A includes the top clamp 13A securing a printed circuit board 15A, the mounting base 12A, and the contact probe 1A via a bottom clamp 14A. The bottom clamp 14A is attached to the top clamp 13A by bolts 17A and bolt holes 16A. The contact probe 1A having wiring patterns 3A (FIG. 110) is pressed by the bottom clamp 14A, so that the wiring patterns 3A press against an IC chip under test while being maintained in a constant inclined state.
FIG. 112 illustrates the probe device 11A of FIG. 111 after assembly. FIG. 113 is a sectional view taken along a line E—E of FIG. 112. As shown in FIG. 113, the front ends of the wiring patterns 3A are brought into contact with an IC chip I by the mounting base 12A. The mounting base 12A is provided with positioning pins 18A for adjusting the position of the contact probe 1A, and the wiring patterns 3A. Thus, the IC chip I can be accurately positioned by inserting the positioning pins 18A into the positioning holes 4A of the contact probe 1A. Elastic bodies 20A of the bottom clamp 14A are pressed against portions of the wiring patterns 3A at windows 19A provided in the contact probe 1A. In this way, the wiring patterns 3A at the windows 19A are brought into contact with electrodes 21A of the printed circuit board 15A forming a signal path by which signals obtained from the wiring patterns 3A can be transmitted via the electrodes 21A of the printed circuit board 15A.
However, the above-described conventional contact probe 1A has the following problems. As shown in FIG. 114, the contact pins 3aA of the conventional contact probe 1A are attached on one face of the resin film 2A. However, the resin film 2A is fabricated from, for example, polyimide resin and therefore, the resin may be elongated by absorbed moisture changing an interval t between the contact pins 3aA. Accordingly, the contact pins 3aA may not accurately contact pads of an IC chip, or device under test, etc. and therefore, an accurate electrical test cannot be conducted. Furthermore, although the positioning holes 4A for integrating the contact probes 1A to the probe device 11A are provided in the resin film 2A of the contact probe 1A, the resin film 2A has a small hardness value and accordingly, the positioning holes 4A are susceptible to being deformed. Therefore, accurate positioning of the contact probe 1A cannot be performed.
Furthermore, according to the contact probe 1A (FIGS. 110–113), during testing of a device, an amount of pressure applied to contact pins of the contact probe is increased or decreased to provide a desired contact pressure. A large amount of pressure must be applied to the contact pins in order to provide a large contact pressure. However, according to the first type of contact probe, front end portions of wiring patterns of the contact probe are used to form the contact pins. The contact pins are made from a material such as Ni (nickel). Therefore, a hardness of the contact pins is typically about Hv 300. Due to the low hardness of the contact pins 3aA, the contact pins may be bent or deformed under excessive contact pressure. Accordingly, there is a limited amount of pressure that can be exerted on the contact pins so that a large contact pressure cannot be obtained. Therefore, a sufficient contact pressure cannot be obtained during electrical measurements of a device under test, resulting in contact failure.
To solve the above problem, there is provided a means of adding an additive agent, such as saccharin etc. in the Ni plating of the contact pins. Although at normal temperature the contact pins have a hardness of Hv 350 or more, the hardness of the contact pins drops rapidly to Hv 200 or less when the contact pins are heated to a high temperatures (e.g., 300° C.). This is due to the S (sulphur) content of the additive agent, such as saccharin etc. which reduces the contact pin hardness at high temperatures. Therefore, the above-described contact probe cannot typically be used at high temperatures, particularly when the contact probe is used as a chip carrier for a burn-in test, etc. which subjects the contact probe to high temperatures.
In addition, surfaces of respective terminals (pads) of an IC chip, etc. are typically made from a material, such as an Al (aluminum) alloy, etc. When such terminals are exposed to air, oxidation occurs and the terminals have a thin aluminum oxide film formed thereon. Therefore, during electrical testing, the aluminum oxide film formed on the surface of the pads of an IC chip, etc. must be removed in order to expose an aluminum matrix underneath the surface so as to ensure proper electrical conductivity between the pads and the contact pins. Accordingly, the contact pins of a contact probe are overdriven while being brought into contact with the surfaces of the pads (e.g., the contact pins are pulled across the pads during contact) so that the aluminum oxide film on the surfaces of the pads is scrubbed off by front end portions of the contact pins exposing the internal aluminum matrix of the pads. The above-described operation is referred to as scrubbing and is important for ensuring proper contact between the contact pins and the pads of the IC chip, etc. during electrical testing thereof.
In performing the scrubbing operation, it is necessary to prevent the contact pins from damaging the aluminum matrix underneath the aluminum oxide film on the surfaces of the pads. Accordingly, in fabricating the contact pins, a mask exposure technology is used and the front end portions of the contact pins are formed having circular arc (convex) faces in a plane view. This is due to the fact that it is difficult to form a fine pattern on a mask in accordance with a desired shape (see FIG. 110). In contrast, a conventional tungsten needle has a planer front end face due to a polishing operation which is performed on the front end portions of the needles in order to adjust the lengths of the respective needles. However, the above-described contact pins are provided with a convex circular face resulting in a small contact area with the pad of the IC chip, etc. so that the contact pins exert a large contact pressure on the pad due to the small contact area. Accordingly, the contact pins are liable to scrape off the aluminum matrix of the pad during the scrubbing operation as compared with the conventional tungsten needle contact probe.
Therefore, it is necessary to ensure a large enough contact angle of the contact pin with respect to the pad so that the aluminum matrix of the pad is not damaged during the scrubbing operation. This is due to the fact that when the contact angle is small, an amount of removed aluminum at the surface of the pad can significantly increase resulting in damage to the aluminum matrix of the pad. However, contact pins 3aA which are formed from a resin film 2A project along a face of the resin film 2A and the contact angle of the contact pin cannot be greater than the angle of the face of the resin film 2A (see FIG. 110). In other words, the angles of the contact pins 3aA are restricted by the angle of the face of the resin film 2A. Therefore, the angles of the contact pins 3aA cannot be set independently from the surface of the resin film 2A.
In the contact probe described above, it is possible to increase the contact angle of the contact pins by increasing the angle of the face of the resin film by devising a way of integrating the contact probe in a probe card which sets the angle of the resin film and the contact pins. In such a case, the scrubbing distance (i.e., length for scrubbing off a skin along the surface of the pad) is extended and depending on a magnitude of the contact angle since the contact angle determines how far the front end portions of the contact pins project over the pads during the scrubbing operation. For example, in the case of a pad having a substantially square form in a plane view with a sides of approximately 90 μm to 100 μm in length, when the scrubbing distance is set to 8 μm with an amount of overdriving of 75 μm and a contact angle of 15° to 20°, even with a slight increase in the contact angle of 5°, the scrubbing distance becomes 12 μm or more.
Furthermore, when the angle of the face of the resin film is increased as described above, the resin film is raised with respect to the contact face by an amount of the angle. In such a case, the resin film and contact probe constitute a probe device which is integrated with various mechanical parts to form a probe card (or prober). When the angle of the resin film is increased, the height dimension of the probe device also increase. However, the above-described probe device is mounted in a prober and the prober cannot be typically made so that it is of a variable height (i.e., a distance/height from the IC chip etc.). Therefore, when the height of the probe device exceeds a predetermined level, the probe device cannot be mounted in the prober.
However, the following problems remain in the above-described contact probe and probe device including the contact probe (contact probe 1A, FIGS. 110–113). Connection from electrodes of the IC chip I to the electrodes 21A of the printed circuit board 15A is conducted via the wiring patterns 3A integrated on the resin film 2A. Therefore, there is no degree of freedom in the pad arrangement of the electrodes 21A on the side of the printed wiring board 15A. Although no particular problem is caused in the case where the electrodes of the IC chip I are arranged uniformly at four sides thereof, it is difficult to deal with the case where the electrodes are arranged nonuniformly on the four sides. In other words, in the case where the electrodes are concentrated on one side of the IC chip, for example, in the case of a driver IC of an LCD, etc. (i.e., several hundreds pins are formed on the longer side of a 3 mm×1 mm size chip), there is no space for arranging pads of the electrodes 21A on the printed circuit board 15A. Therefore, it is difficult to connect the electrodes of the IC chip I to the printed wiring board 15A.
According to the previously described contact probe 1A, one side of the contact probe is typically arranged to align with the pad positions of an IC chip, etc., while the other side is connected to the printed wiring board 15A. In order to widen the pitch of the wiring patterns 3A of the contact probe 1A, the contact probe 1A is formed in a trapezoidal shape (see FIGS. 110–113). Furthermore, positioning holes 4A are provided in the contact probe 1A and the contact probe 1A is integrated with highly accurately fabricated mechanical parts by using the positioning holes 4A. In this way the mechanical parts are integrated with the printed wiring board 15A. In addition, according to the contact probe 1A, a photolithography technology capable of finely forming patterns is used for a fabricating and forming process of the wiring pattern 3A. Therefore, the contact probe 1A, advantageously, provides a narrowed pitch front end portion so that the contact probe 1A can be brought into contact with the narrow pitch of the contact pads of a device under test.
However, the accuracy of positioning the contact pins 3aA of the contact probe 1A with respect to the contact pads of an IC or an LCD, is dependent upon the accuracy of the fixing means with respect to the mechanical parts. In other words, the accuracy of fasteners using the positioning holes 4A. Accordingly, even if the pitch of the contact pins 3aA is narrowed or the diameter of the front end of each of the contact pins 3aA is considerably diminished, when the accuracy of positioning is poor, it is difficult to take advantage of the advantages of the contact probe 1A.
Furthermore, there are the following additional problems in the contact probe 1A. According to the contact probe 1A, the front end is provided with a portion where the pitch of the wiring patterns 3A is narrowed. Therefore, the yield is lowered in the photolithography or plating step, etc. used in fabricating the contact probe 1A due to the narrow pitch area. This means that in fabricating the contact probe 1A, the yield of the contact probe 1A is governed by the yield of the portion where the pitch is narrowed. In this case, the contact probe 1A is formed in a trapezoidal shape with the narrower front end portion having the narrower pitch wiring patterns 3A and the wider rear end portion having wiring patterns 3A that are coarse. Moreover, in integrating the contact probe 1A to the printed wiring board 15A, a considerably large area is required to accommodate the contact probe 1A. In this case, a necessity of a large area for the contact probe 1A results in a small number of the contact probes 1A being able to be formed from a resin film 2A used as a raw material and having limited area. Therefore, when the above-described contact probe 1A is fabricated, the yield is governed by the front end portion having the narrow area with the narrow pitch wiring, while the area per se of the contact probe is governed by the wider portion with the coarse pitch wiring.
Furthermore, in relation to the above-described problems, the front end portion or contact pin of the contact probe 1A is liable to be destroyed since the contact pins project from the resin film 2A. In this case, the entire contact probe 1A must be replaced even if only one contact pin is damaged. Accordingly, maintenance costs of a probe device using the contact probe 1A increase. Furthermore, the above-described contact probe 1A does not allow for ease of changing contact pressure of the contact pins.
A conventional probe card is shown in FIG. 116. According to the probe card, perforated portions are provided at measurement positions of the card comprising a glass epoxy plate with contact pins (needles) projecting from the measurement positions. A material, such as W (tungsten) having a small degree of wear is generally used as the material for fabricating the needle. The probe card is provided in a shape of a leaf spring where the contact pins are extended toward a direction inclined downwardly and is referred to as a horizontal arranged needle type probe card. In addition, as illustrated by FIGS. 115(a) and 115(b), terminals to be inspected by the probe card are peripherally arranged, wherein terminal electrodes are formed only at a periphery of a chip (FIG. 115(a)), and planarly arranged, wherein terminal electrodes are formed over the entire face of the chip (FIG. 115(b)). In this case, although the above-described horizontal arranged needle type probe card can deal with the peripherally arranged terminals, it cannot deal with the planarly arranged terminals. Furthermore, there is a limitation in multi pin formation of the probe card. In addition, according to the horizontal needle arranged type probe card, the total length of the contact pin is typically 40 mm to 30 mm. Therefore, there is a limitation in an inspection speed using the probe card. Hence, a vertically arranged probe card was devised as shown in FIG. 117 to overcome the deficiencies of the above-described horizontally arranged needle type contact probe. According to the vertically arranged type probe card, the card can deal with the planarly arranged terminals, multi pin formation can be realized, and the problem of the inspection speed is also improved since the length of the contact pin is approximately 11 mm to 7.5 mm which is comparatively short.
However, the vertically arranged type probe cards have the following problems. When there is a more or less a deviation with the respective total lengths of the contact pins, if all of the contact pins including contact pins of various lengths are brought into contact with respective terminals, the longer contact pins are bent during an overdriving operation (i.e., contact pins are pulled down further than from where they are brought into contact with the terminals). According to the above-described probe card, the material of the contact pins is tungsten which is highly rigid. Therefore, in overdriving the contact pin, the longer contact pins are not sufficiently bent and the shorter contact pins are not firmly brought into contact with the terminals. Particularly, in the case of the vertical needle type probe card, the contact pins are brought into contact with the terminals substantially in a vertical direction which makes the contact pins less likely to bend. In addition, the above-described contact pins made of tungsten are devoid of flexibility. Therefore, even if they are bent, the direction of bending does not stay constant. As a result, contiguous ones of the contact pins may erroneously be brought into contact with each other causing shorting between contact pins. Also, according to the above-described needle type contact probe, the integration of the contact pins, alignments of the heights and the positions of the respective pins must be performed manually, which is very difficult. Furthermore, it is difficult to deal with the multi pin and narrow pitch formation due to the limitation in the diameter of the tungsten needle.